(a) Field of the Invention
The present invention relates to a switch control device. More particularly, the present invention relates to a switch control device that controls a switching operation of a power switch that supplies a high-voltage.
(b) Description of the Related Art
A switch control device that controls a switching operation of a power switch is supplied with power for operation. In general, the switch control device senses a power voltage and does not operate when the power voltage is lower than a predetermined low voltage. This is because that the switch control device may malfunction if the power voltage is low.
However, when the power voltage is decreased lower than a low voltage, the switch control device may not sense the decrease of the power voltage so that an output of the switch control device may be latched. Particularly, when the output of the switch control device is latched to a level that turns on the power switch, the power switch may be damaged or excessive power may be supplied.
In further detail, when the power switch is a high-voltage power switch that supplies power to a load from a high-voltage side and the output of the switch control device is latched to the level that turns on the power switch, excessive power is supplied to the load from the high-voltage, and a current flowing to the power switch may cause generation of excessive heat. The heat may cause damage not only to the power switch but also the switch control device that controls the power switch.
FIG. 1 shows a case that the output of the switch control device is latched when the power voltage is decreased lower than the low voltage. A gate signal OUT is a signal that turns on/off the power switch.
As shown in FIG. 1, a gate signal OUT is synchronized with an ON pulse and thus increased to a high level, and is synchronized with an OFF pulse and thus decreased to a low level. The power switch is turned on by a high-level gate signal, and is turned off by a low-level gate signal.
The ON pulse and the OFF pulse in the switch control device are generated by the power voltage. However, when it is not sensed that the power voltage is decreased lower than the low voltage (hereinafter, an abnormal state), the switch control device performs normal operation. Then, the decreased power voltage generates a low ON pulse and a low OFF pulse.
Particularly, when the power voltage is decreased to a transmission voltage VTRAN that is lower than the low voltage at a time point T1, an ON pulse or an OFF pulse generated after the time point T1 is not recognized as an ON or OFF pulse in the switch control device so that the gate signal is not changed according to the ON or OFF pulse.
The transmission voltage VTRAN implies a minimum voltage that can be recognized in the switch control device. That is, a voltage higher than the transmission voltage VTRAN in the switch control device is recognized such that it has an influence on the operation of the switch control device. However, a voltage that is lower than the transmission voltage VTRAN does not have any influence on the operation of the switch control device. Thus, when the ON pulse or the OFF pulse is lower than the transmission voltage VTRAN, the switch control device cannot recognize the ON or OFF pulse.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.